H3 Tags

Hey, I’ve set up a custom Heading 3 header, but I was wondering how I can also add the H3 tags to text when I apply the heading?
I need to deliver client work in Google Docs, so I’d just like to be able to copy and paste from Scrivener into Docs and have the Heading 3 automatically apply like H1 & H2 does.
Please help, thanks!